1. Field of the Invention
The present invention relates to display devices and methods of driving the display devices. Specifically, a method of improving the quality of moving images in the hold-type display devices.
2. Description of the Related Art
In recent years, there has been growing interests in thin display devices. As substitutes for CRT displays, liquid crystal displays, plasma displays, projection displays, and the like have been developed and becoming popular. Furthermore, field emission displays, inorganic electroluminescence displays, organic electroluminescence displays, electronic paper, and the like have been developed as next-generation display devices.
In a display portion which is provided in the above-described display device, pixels which are minimum units for constituting an image are disposed. Each of the pixels emits light with certain luminance in accordance with the image data to display an image in the display portion.
When a moving image is displayed in such a display device, different images are displayed quickly, several tens of times per second. The period in which an image is displayed is referred to as one frame period.
Here, driving methods of display devices can be classified according to temporal distribution of the luminance of a pixel in one frame period. As for the hold-type driving, the luminance of a pixel is almost constant in one frame period. On the other hand, as for impulsive-type driving which is typified by CRT, after intense light is emitted once in one frame period, the luminance of a pixel immediately decreases and light is not emitted any more. In impulsive driving, a non-lighting state dominates the most part of one frame period.
Unfortunately, hold-type display devices have motion blur in which in displaying moving images, a part of the moving image appears to have traces or the whole image is blurred. This is because an image displayed on a hold-type display device is kept still during one frame period, while a man turn his eyes in the direction in which the image move, while predicting the movement of the image. This leads to mismatching between the movement of human eyes and the movement of moving image. On the other hand, in an impulse type display device, an image appears in an eye's blink and immediately disappears, there is no problem of such mismatching between human eyes and an moving image, which does not lead to motion blur.
Typically, two methods for solving the problem of the hold-type display device are proposed (Patent Document 1: Japanese Patent No. 3295437). The first method is a method in which a period for displaying an image and a period for display a black image are provided in one frame period. By this method, the display can become pseudo impulse type display, afterimages can be made less easily perceived and moving image characteristics can be increased. (Patent Document 2: Japanese Published Patent Application No. H9-325715 and Patent Document 3: Japanese Published Patent Application No. 2000-200063). The second method is a method in which one frame period is shortened (in other words, the frame frequency is made large), thereby the movement of an image follows the movement of human eyes to smooth the movement of the image, which leads to improvement of moving image characteristics (Patent Document 4: Japanese Published Patent Application No. 2005-268912). Further, as the improvement of the first method, a method in which in stead of the black image, an image which is darker than an original image is displayed to improve the moving image characteristics is known (Patent Document 5: Japanese Published Patent Application No. 2002-23707. Patent Document 6: Japanese Published Patent Application No. 2004-240317, Non-patent document 1: Society For Information Display '05 DIGEST, 60.2, pp. 1734-1737 (2005), Non-patent document 2: Society For Information Display '06 DIGEST, 69.4, pp. 1950-1953 (2006), Non-patent document 3: Society For Information Display '06 DIGEST, 69.5, pp. 1954-1957 (2006)). Further, a method in which a driving method is changed depending on the movement amount of an image, or a temperature is known (Patent Document 7: Japanese Published Patent Application No. 2002-91400, Patent Document 8: Japanese Published Patent Application No. 2004-177575).